Flowmeters measure the rate of flow of a fluid in a pipe or other pathway. The fluid may be, for example, a gas or a liquid, and may be compressible or incompressible. One type of flowmeter is a vortex flowmeter, which use the principle of vortex shedding to measure flow rate. Vortex shedding refers to a process in which a fluid passing a bluff body (sometimes referred to as a shedder) causes a boundary layer of slowly moving fluid to be formed along the surface of the bluff body. A low pressure area is created behind the bluff body and causes the boundary layer to roll up and form a vortex. This process is repeated and results in a series of vortices in succession on opposite sides of the bluff body. The vortices can be detected using one or more of several different measurement principles. In one example, a pressure sensor detects the pressure effects of the vortices. The frequency at which the vortices are generated is related to flow rate. Vortex flowmeters are considered linear flowmeters, as the measured vortex frequency varies generally linearly with volumetric flow rate. Accordingly, by measuring the frequency of the pressure variations associated with the vortices, the flow rate may be determined.
Vortex flowmeters provide vortex frequency data that can be used in conjunction with flow calibration factors to determine the velocity and volumetric flow rate of the fluid passing through the meter. “Intelligent” vortex flowmeters locally perform the calculations necessary to convert the frequency data into an indication of flow rate. Some intelligent vortex flowmeters, called multivariable meters, are capable of receiving additional measurement data (e.g., temperature or line pressure signals) and using that data to improve the traditional flow rate measurement. For example, calibration factors are assumed constant in many conventional flowmeters. However, in multivariable meters that are configured to receive a temperature signal, these calibration factors can be compensated for changes in temperature. Likewise, temperature and/or pressure signals may be used to determine a fluid density measurement that can be combined with the volumetric flow rate to produce a mass flow measurement. These measurements, and others, can be transmitted to a control room or other receiver over a communication line, such as, for example, a standard two-wire 4-20 milliamp (“mA”) transmission line, wireless transmission, and others.
Accordingly, an improved multivariable vortex flowmeter configuration is desired.